This invention relates to an apparatus for automatically measuring values proportional to impedance components of biological objects, particularly of live tissues, using a high frequency current source connected to a series combination of two equal resistances and of the measured object, which apparatus enables a simultaneous reading to be made of two values at the moment the applied voltage reaches a required value.
A certain impedance of a biological object, as for instance of a live tissue, opposes the passage of an alternating current connected thereto: This impedance has a resistive, a capacitive and an inductive component. The inductive component of live tissues is so small, that it can be neglected from further considerations. The measuring of the resistive and capacitive component of the impedance is accomplished by connecting the investigated live tissue by means of point shaped electrodes together with two equal resistances in series to the terminals of a high frequency current source. The voltage both across the series combination resistance - tissue and across the tissue proper is measured by an electronic voltmeter at a certain level of the supplied high frequency voltage. The obtained voltages are proportional to the required components of the impedance. The absolute values of the components of the impedance can be relatively easily calculated from the measured values, but generally this is not necessary. The measurement is performed at a constant applied voltage and the measured values are sufficiently illustrative for the studies of physiological conditions of the investigated tissue.
A drawback of this process, however, is that the proper measurement must be performed by at least two persons, particularly when investigating tissues of living beings. One person has to take care of the manipulation with the electrodes, the second person attends to the measuring apparatus. The obtained results are, in addition, burdened by a certain error, as at actually used arrangements a simultaneous reading of two different voltages at the moment of an accurate adjustment of the required applied voltage cannot be secured even in the case of the simultaneous use of two measuring apparatus or of one measuring apparatus with the possibility of switching over from one voltage being measured to the other.